Study of the dominant luminescence mechanism in InGaN/GaN multiple quantum wells comprised of ultrasmall InGaN quasiquantum dots

High quality green (508 nm) and blue (424 nm) light emitting diodes (LEDs) from InGaNGaN multiple quantum wells with stable ultrasmall indium-rich clusters of 2 nm and 3 nm from two different nominal indium contents have been grown by metalorganic chemical vapor deposition. Comprehensive calculations including polarization, piezoelectric field, and size effect help derive an indium composition of 59% and 31% for the In-rich clusters of 2 nm and 3 nm, which agrees amazingly well with the asymmetric phase diagram for phase separation. From this model, we can further demonstrate that the dominant emitting mechanism for green LED is the polarization field, however, for blue LED, both the size effect and polarization effect are equally important.